1. Field of the Invention
The present invention relates to an air-conditioner having a dual-refrigerant cycle and, more particularly, to an air-conditioner having a dual-refrigerant cycle capable of enhancing efficiency of an air-conditioner by compressing a refrigerant by using a compressor in a secondary refrigerant circuit.
2. Description of the Related Art
In general, a heat pump type air-conditioner, which performs both cooling and heating operation, can be used both as a cooling device by including an indoor heat exchanger and an outdoor heat exchanger and as a heating device by reversing flow of a refrigerant of a refrigerant cycle.
An air-conditioner having a dual-refrigerant cycle is constructed such that a refrigerant circulation circuit of the outdoor unit and an indoor unit is separated, so a primary refrigerant circuit is provided in the outdoor unit while a secondary refrigerant circuit is provided in the indoor unit. A heat exchange unit for heat exchanging is disposed between the primary and secondary refrigerant circuits.
FIG. 1 shows the construction of a refrigerant cycle of the air-conditioner having the secondary refrigerant circuit in accordance with a related art.
The related art air-conditioner includes: a primary refrigerant circuit 102 heat-exchanged with outdoor air; a secondary refrigerant circuit 104 heat-exchanged with indoor air to perform a cooling and heating operation; and a heat exchange unit 106 disposed between the primary and secondary refrigerant circuits 102 and 104 and performs heat exchanging therebetween.
The primary refrigerant circuit 102 includes an outdoor heat exchanger 108 heat-exchanged with outdoor air; a four-way valve 110 changing a flow of a refrigerant in a forward direction or in a reverse direction; an expansion valve 112 disposed at a refrigerant pipe 130 connected between the outdoor heat exchanger 108 and the heat exchange unit 106 and changing a refrigerant to have a low temperature and low pressure, a compressor 114 for compressing a refrigerant to have a high temperature and high pressure; and an accumulator 118 connected with a suction side of the compressor 114, separating the refrigerant into a gas and a fluid, and supplying a gaseous refrigerant to the compressor.
The secondary refrigerant circuit 104 includes a plurality of indoor heat exchangers 122 connected with the refrigerant pipe 120 constituting a closed circuit and heat-exchanged with indoor air, and a pump 124 installed at the refrigerant pipe 120 and pumping the refrigerant so as to circulate the secondary refrigerant circuit 104.
The refrigerant pipe 130 of the primary refrigerant circuit and the refrigerant pipe 120 of the secondary refrigerant circuit 104 are connected with the heat exchange unit 106, whereby the heat exchange unit 106 allows heat exchanging between the primary refrigerant circuit 102 and the secondary refrigerant circuit 104.
The operation of the related art air-conditioner constructed as described above will be explained as follows.
FIG. 2 is a graph showing pressure-enthalpy loops of the primary and secondary refrigerant circuits when the air-conditioner is operated for heating in accordance with the related art and FIG. 3 is a graph showing pressure-enthalpy loops of the primary and secondary refrigerant circuits when the air-conditioner is operated for cooling in accordance with the related art.
First, the operation of the primary refrigerant circuit during a heating operation is as follows.
A refrigerant is compressed in the compressor 114 (D→C process). The compressed refrigerant is heat-exchanged and condensed while passing through the four-way valve 110 and the heat exchange unit 106 (C→B process). And then, the refrigerant is changed to a low temperature and low pressure fluid refrigerant while passing through the expansion valve 112 (B→A process). Thereafter, the refrigerant absorbs latent heat of vaporization while passing through the outdoor heat exchanger 108 so as to be evaporated (A→D process). And, the evaporated refrigerant is introduced into the accumulator 118 through the four-way valve 110 so as to be separated into a gas and a fluid, and the gaseous refrigerant is supplied to the compressor 114. In this manner, the refrigerant is circulated.
The operation of the secondary refrigerant circuit during a heating operation is as follows.
A refrigerant flowing through the refrigerant pipe 120 performs a heating operation while passing through the indoor heat exchangers 122 (4→1 process). After finishing the heating operation in the indoor heat exchangers 122, the refrigerant is pumped by the pump 124 to obtain a driving force to circulate through the refrigerant pipe 120 (1→2 process). The pumped refrigerant is heat-exchanged with the primary refrigerant circuit 102 while passing through the heat exchange unit 106 (2→3 process). The heat-exchanged refrigerant is supplied to the indoor heat exchangers 122 (3→4 process).
The operation of the primary refrigerant circuit during a cooling operation is as follows.
When the four-way valve 110 is operated, the refrigerant flow passage is changed and the refrigerant is compressed in the compressor 114 (D→C process). The compressed refrigerant is heat-exchanged and condensed while passing through the four-way valve 110 and then the outdoor heat exchanger 108 (C→B process). The condensed refrigerant is expanded to be a low temperature and low pressure liquid refrigerant while passing through the expansion valve 112 (B→A). The expanded refrigerant is heat-exchanged while passing through the heat exchange unit 106 to absorb latent heat of evaporation so as to be evaporated (A→D process). And then, the refrigerant is separated into a gas and a fluid while passing through the four-way valve 110 and the accumulator 118, and the gaseous refrigerant is sucked into the compressor 114. These processes are repeatedly performed.
The operation of the secondary refrigerant circuit during a cooling operation is as follows.
The refrigerant absorbs latent heat of evaporation while passing through the indoor heat exchanger 122, thereby performing the cooling operation (2→3 process). And then, the refrigerant is moved into the heat exchange unit 106 (3→4 process). Thereafter, the refrigerant is heat-exchanged with the primary refrigerant circuit 102 while passing through the heat exchange unit 106 so as to be condensed (4→1 process). The condensed refrigerant is pumped by the pump 124 to obtain a driving force to circulate through the refrigerant pipe 120 (1→2 process).
However, the related art air-conditioner has the following problems.
That is, since the condensing process (C→B process) of the primary refrigerant circuit 1020 during the heating operation has a higher pressure than that of the evaporating process (4→1 process) of the secondary refrigerant circuit 104 for actually performing the heating operation in a room, efficiency of the primary refrigerant circuit is degraded.
In addition, since the evaporation process (A→D) of the primary refrigerant circuit 102 during the cooling operation generates evaporation at a lower pressure than that of the condensing process (2→3) of the secondary refrigerant circuit 104 for performing the actual cooling operation, efficiency of the primary refrigerant circuit is degraded.
Accordingly, although the related art air-conditioner having the dual-refrigerant cycle is advantageous in that the compressor oil is not introduced toward the secondary refrigerant circuit 104 because the primary and secondary refrigerant circuits 102 and 104 are separated, the condensing pressure of the primary refrigerant circuit 102 is higher than the secondary refrigerant circuit 104 or the evaporation pressure of the primary refrigerant circuit 102 is lower than the condensing pressure of the secondary refrigerant circuit 104, resulting in degradation of efficiency of the air-conditioner.